Oscillation generator



OS CILLATI ON GENERATOR Filedl Nov. e, 1941v H. 7.' FRI/S /NvE/vroRs y C, R/DEOUT ATTORNEY Patented Aug. 27, 1946 OSCILLATION GENERATOR Harald .T. Friis, Rumson, and Vincent C. Rideout, Red Bank, N. J., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application November 6, 1941, Serial No.` 418,018

4 claims. (ci. 25o-36) Y This invention relates to vacuum tube `oscillators and more particularly to oscillators for the generation of ultra-high frequency currents for which the corresponding wave-lengths may be comparable to the dimensions-ofl the Vacuum tube electrodes and their associated leads.

The principal objects of the `invention are to ensure the establishment of the oscillation frequency at a definite desired value and to prevent the generation of oscillations at frequencies other than that desired. Another object is to improve the efciency of ultra-short wave oscillation of the feedback type.

When the frequency of oscillation corresponds to a wave-length of the order of centimeters it may be found that the distributed inductance and capacity of the vacuum tube electrodes and their lead-in conductors Vare suchlthat a portion of a standing wave representing a-substantial n fraction of a wave-length may be set up within the vacuum 4tube, leaving lonly a small part of the Wave to be established in the conductors eX- -ternal to the tube. This results in a restriction of the range and accuracy of adjustment ofthe oscillation frequency. Where tuning by Lecher wires or adjustable concentric lines has been used, a common practice has been to extend the lengths of the lines sufliciently to include several half waves at the oscillation frequency. This has the advantages of permitting a wide range of frequency adjustment and, because of the inherently low dissipation of the line structures, of ensuring a high degree of frequency stability. However, such arrangements tend to permit the `establishment of oscillations at the lower natural frequencies ofthe extended lines, with the result that oscillation at the desired harmonic modes can be started and rmaintained only with difliculty. Y

In accordance with this invention the abovenoted difficulty is avoided by employing the feedback method of oscillation generation using a triode vacuum tube and by tuning two of the interelectrode circuits by means of lines differing in length by a predetermined fraction of a wavelength at the operating frequency. With this arrangement the phase or the magnitude, or both, of the feedback are such at the lower natural resonances of the lines that oscillations cannot be sustained. For the generation of the highest frequency oscillations we find it advantageous to operate the vacuum tube with its control grid at ground potential and to connect the tuning lines to the grid-cathode and grid-plate circuits, respectively. .The feedback coupling may be provided by the inherent capacity between the plate and cathode or a supplementary capacity may be provided if necessary.

Other features of the invention are, first, the use of a vacuum tube having its electrodes so disposed and connected that they form, vin effect, continuations of the tuning lines and, second, the extension of the tuning lines on both sides of the electrodes. `By virtue of these features the creation of voltage antinodes at the centers of the electrodes becomes possible with a resulting `substantial increase in the output power.

The nature of the invention will be more fully understood from the detailed description which follows and by reference to the accompanying drawing of which:

tion;

Figs. 2 to 4, inclusive, areV diagrams illustrative of the operation of the invention;

Fig. 5is a somewhat simplified showing of a preferred form of the invention; and

Figs. 6 and 7 illustrate mechanical and circuit features of the oscillator of Fig. 5.

Referring to Fig. 1, III is a vacuum tube containing a straight lamentary cathode II, a control grid I2, and an anode I3, disposed in parallel relation to one another. Lead-in wires ex- Itend from both ends of the filament and plate through opposite sides of the tube to tuningconductors I4, I5, I6 and I1, which constitute the centralconductors of sections of coaxial line elements I8, I9, Z0 and 2|. Each line section is provided with a sliding short-circuiting bridge such las 22, by .means of which its effective length may be varied for tuning purposes. For the sake of simplicity the connections of the energizing sources for the cathode and plate have been omitted from the showing of Fig. 1, but these are shown in Fig. 5. As is usual in thecase of feedy back oscillators, the plate is positive with respect to the filament and thegrid may beat the same direct current potential as the filament or .may be given a negative bias.

vided bythe direct capacity between the plate Fig. 1 is a simplified schematic of the inven- The control gridis connected directly to the outer conductors of the atively to the mid-point of the tube electrodes thatrvcltage antinodes exist at the centers of the plate and filament when standing waves are pro- Y duced. With these adjustments rthe system oscil" lates readily at the desired frequency-correspond-V ,v ing to the half Wave diiTerence inthe lengths of y Y Y' Y v shown inlFigs. 5, ,6 and 7. Referring tc Fig. 5,

`Ythe vacuum tube comprises a roughly hemispherical glass envelope 23 sealed to a iiat metallic the lines.

'Ihe oscillatormay be looked upon as a modilied form of the well-known C'olpitts oscillator,

in which the oscillation circuit comprises essentially two capacities interconnecting the`r grid and cathode and the plate and cathode, respectively, and an inductance ,connected betweenrpthe plate and the grid. One of the capacities is provided'by the plate to cathode tube capacity/1Ds and the other by detuning the cathode line lil, Vl 9 to-a frequencyavery slightlybelcw` the oscillation frequency so -thatits eiective reactance,

measured at Ythe tube electrodes, is capacitive.

Correspondingly, the, inductive characterof the plate to'grid impedance maybe realized by Vtuning Vthe.' plateline 2,53, 2l to a frequencyveryslightly greater than-the oscillation frequency. `Y`This. ex Yplanatio'nof Vthe, character of the. Circuit isV given tentatively in Vthe absence Yof, more'vlexaot knowledge .of theactions atltheextremely high, fle quencies contemplated.Y

Some of the various standing waveY conditions v that mayY existinthe tuninglines of tlfieoscillar the" electrodeY structures the voltage' distributionV maybe. expected to diier from the simple sinuso idal Aform characteristic of .a uniform line. With this mode Vof operation the range of adjustment is limited Yby the dimensions of the tube and the highest frequenciesA cannot bel produced.

Fig. 3 illustrates one mode of operation in ac'- cordance withthe invention. The plate Aline extendedA on both sides of the tube sufficiently Ato accommodate three half waves and the y fila- Qment line is4 extended on one side only so thatl it includes two half Waves.. VI'f the lament line wereY extended equally on the other side of the tube, oscillation could take place at a greater Wave-length as indicated, by the dotted curves, but, with the two linesv V'differing by one-half wave-"en gth, oscillation is possible only at rthe a higher frequency.

` For the generation of the highest possiblefrequencies it is desirable that each, of thel lines shou1d include at least three half Waves', in

which case the dimensions of theV tube no ylonger limit Vthe .positioning of the `shortcircuiting bridges.` Fig. i illustrates the'stand'ingwaveconditionswher the filament line includes threeA half waves vand the plate line includes four.

4 Under this condition the short-circuiting bridges can be kept well clear of the tube structure so that the tuning adjustment is not restricted. ,Y

It will be evident that the lines might be extended further to include larger numbers of half waves andthat the difference in their lengths ceuld be'inore than a single half wave, subject to` the condition that the dilerence should not be such as to permit oscillationsin a lower frequency mode.

onstructional features of an oscillator Y,embodying,the principles .of the invention areV .base 2d. v'The grid l2 is mounted directly on the base .2d and is electrically connected thereto.

Leads from both ends of filament i! and plate tirare brought out through vglass seals,v,such as 25, ineholes in the base', The four tuning linesAV I3, le, 29 Yand 2lY haveA their outer conductors connected directly to the vacuumtube b ase 'Ell 'and extend perpendicularly thereto, The

inner conductors Y*of the'li'nesconsist of smallY diameter tubes such as 25, the o uter surfaces of which carry Ythehigh.'frequency' currents and through which insulated conductorsarethreadedV forsupplying the necessary energizing currents to the plate" and flarnent.V These 'inner 'tubes areY held Yin place insiderthe outer conductors by ring" supports such as 2'! which may `be metallic. At'their inner ends, the inner tubes arev provided with special condenser couplings te 'to ther/u1-` rent supply conductors top-rovide low impedance paths for the high frequency oscillations. These are shown diagrammatically in'Fig.'5 and indetail in Fig; 7. Adjustment of the eifective lengths of the linesV is obtained by meansrof sliding bridges such as 28 comprising metallic piston members drilled through the'center to' slide' over the'inner tubes and provided with a circular comb of nexible contact fingers which make cone tact with both line conductors. Direct current is supplied to 'the plate from a source through the inner conductor ofA line 2Q. The "other terminal of the plate` extends into the inner conductor ofline 2l but is insulated therefrom bycondenser coupling 30. Filamentcu'rrent 'is supplied from a sourceV 3l, grounded atits positive terminal,`

through conductors threading the inner tubes of lines I3 and lil and is controlled by a circuit including resistors 32 and 33, potentiometer 34, and ballast lamp 35. These elements also serve to provide a suitable Ynegative bias Yvoltage for the grid, the amount of which may beV controlled by the choice vof the values of resistors 32 and 33. An output circuit isindicated by a branching concentric line 36 connected to line 2E) .close to the base of the tube. When this output circuit connection is used the impedance ofthe connected circuit should be high and preferably should be so tuned as to prevent any substantial effect on the standing wave pattern in the oscillator lines. Other well-known types of coupling may also be used.

As already explained, the showing of Fig. 5 is to some extent diagrammaticY Constructional features of an actual oscillator are shown in Figs. 5 and A'2.

The vacuum tube plate I3 has a roof-like form in section and a diamond-shaped plan. Th'e grid has the sectional form of a U-shaped channel and has a multiplicity of narrow transverse slits, not shown, giving it a comb-like structure.

Short tubular elements 31 welded to the tube base plate provide supports for the tuning lines. The lines fit over the supporting elements, good contact and a firm hold being obtained by slitting the ends of the outer conductors axially. Oth'er familiar methods of attachment may, of course, be used. The tube terminals take the form of straight rods coming out through the centers of the line supporting tubes. Their connections to the inner conductors of -the tuning lines and the power supply leads are shown in detail in Fig. '7. Plate supply lead38, passing through the center of the inner conductor and insulated therefrom by glass beads 39 terminates in a tapered circular rod 40 which fits tightly in the end of the inner conductor tube and is insulated therefrom by a layer of mica 4I. 'I'he end ,of the rod 40 projects beyond the inner conductor tube and is drilled and slitted axially to receive and make contact with plate terminal 42. The layer of mica between the terminal rod and the tube insulates the direct current supply circuit and at the same time provides a capacitive coupling to the tubular conductor having very low impedance at ultra-high frequencies. The connections to the other terminals of the tube are made in the same way as described above.

For the adjustment of th'e short-circuiting bridges 28, rods 43 are provided which are connected to the bridges and extend beyond the ends of the tuning lines.

What is claimed is:

1. An oscillation generator comprising a vacuum tube having a cathode, an anode and a control grid, a tuning line connected to said anode and said grid and a second tuning line connected to said cathode and said grid, said lines being short-circuited at their ends remote from the vacuum tube electrodes and having unequal lengths differing by an integral number of h'alf wave-lengths at the oscillation frequency, and said electrodes being connected to said lines at points corresponding to voltage loops of the standing waves developed in the lines at the oscillation frequency.

2'. An oscillation generator in accordance with claim 1 in which the tuning lines are extended on both sides of the vacuum tube electrodes suiiiciently to include on each side at least one half standing Wave in addition to th'e half wave centered about the connection of the electrodes to the lines.

3. An oscillation generator in accordance with claim 1 in which the tuning lines are extended o-n both sides of the vacuum tube electrodes and in which the electrodes are connected to the line extensions at the opposite ends of their major axes whereby the electrodes are included as portions of the line conductors.

4. An oscillation generator in accordance with claim l in which the tuning lines comprise coaxial conductors, the cathode of the vacuum tube being connected to the inner conductor of one of said lines, the anode being connected to the inner conductor of the other line, and the control grid being connected to the outer conductors of both' of said lines.

HARALD T. FRIIS. VINCENT C. RIDEOUT. 

